Using sensitivity of the CTE to calculate sample size, the planned sample size for this study is 163 subjects. The study will be powered at 80% to demonstrate that the lower radiation CTE (ASIR and MBIR) is non-inferior (type I error rate of 2.5%, one sided) to the standard CTE. The sensitivity of the standard CTE is assumed to be 0.77 based on a pooled estimate [7]. 0.1 is chosen as the non-inferiority margin. The correlation between the two procedures is considered in the sample size calculation. We assume that the prevalence of Crohn's Disease is 80% among the target population.